The body to frame mounting assembly is used to attach automotive body parts to a frame so that the two metal components do not directly contact one another, as a direct contact would provide a high degree of noise transmission from one component to another, as well as a direct transmission of vibration and other mechanical actions. Conventional body mount assemblies, compression or shear type, utilize multiple or single elastomeric members to isolate the frame from the automotive part to be mounted on the frame. Since both the frame and the automotive part are isolated from one another and from the fastener system joining them, the transmission of noise and vibration from the frame to the automotive part is minimized.
Controlling the design and material properties of typical body mounts, in reference to noise and vibration transmission to vehicle occupants, is only one, of many, paths that development engineering can take to address a total vehicle noise and vibration issue. Ultimately, the body mounting system is the direct transmission source of noise and vibration to the occupant compartment. Thus maintaining a body mount design that controls body movement and appropriately isolates the vehicle occupants from noise/vibration is challenging
In the design of automotive vehicles, such as pick-up trucks, the final desired vehicle level ride and vibration tuning requirements are complex in that consideration must be given to the multiple wheel base, power train, cab style, and tire/wheel offerings. Proper selection of material and isolator dynamic/static rates for tunable parts; i.e., suspension bushings, power train mounts and the body mounts, is critical when balancing vehicle level ride and vibration performance. Tunable part characteristic selection is one path, of many, that the vehicle engineering development community uses in establishing vehicle level performance attributes. The selected tuning can require multiple parts to support the complex vehicle offerings. Accordingly, while trying to maintain manageable component quantity complexity at the manufacturing facility, some vehicle configurations may not be optimally tuned for the best vehicle level ride and vibration performance. Couple vehicle build variability with individual component assembly variability and an opportunity exists to build a vehicle with less-than-optimal ride and vibration characteristics. At this point in development, time to make component design changes, for production, has elapsed to zero; trying to add more component/system damping becomes increasingly difficult.
The addition of frame mounted tuned mass dampers, to reduce vehicle level vibration sensitivity to Body-on-Frame vehicles, by adding increased levels of system damping, traditionally requires design proveout due to a late discovered issue. The design/development proveout requires a substantial amount of time and manufacturing expense to implement. Furthermore, the addition of mass dampers is effective only in select spots on the vehicle and requires additional development. Since the addition of mass dampers is not planned, the implementation represents a significant amount of additional expense. Generally speaking, frame mounted tuned mass dampers are affective once implemented; however, cost, weight and vehicle assembly are detrimental to the design. As mentioned previously, the output of a tuned mass damper still does not apply the desired damping at the best location; at the body mount positions. As such, hydraulic body mounts have been utilized in automotive vehicles as a replacement for the conventional body mount. These hydraulic mounts now add to the additional body mount/part complexity and also must adhere to the performance criteria of a traditional body mount such as, durable against high vehicle loads associated with vehicle operation, which has resulted in a high failure rate.
U.S. Pat. No. 5,330,166, granted to Hirofumi Aoli on Jul. 19, 1994, discloses a conventional hydro mount having a tunable frequency range that is used for classic engine, body or suspension mounts to replace shear-type body mounts, instead of being used in addition thereto. U.S. Pat. No. 5,529,295, issued to Markus Leibach on Jun. 25, 1996, is directed to an engine mount isolator employing an electromagnetic fluid controlled device to improve the feedback mechanism for an active controlled engine mount system. In U.S. Pat. No. 6,394,432, granted on May 28, 2002, to Gerald Whiteford, a conventional hydro mount system is provided with a compensator device to make up for the inherent shortcomings of the classic hydro mount.
U.S. Pat. No. 6,986,545, issued on Jan. 17, 2006, to Ingemar Nilsson, teaches the use of two isolators; however, the isolators are not joined together. Instead, the two isolators are joined to the same subframe member, but no pumping action from one isolator affects the driving of the other isolator. Accordingly, the Nilsson patent does not disclose a plug-in damper that is supplemental to the operation of the conventional isolator. In U.S. Pat. No. 7,036,803, issued to Clayton Maas on May 2, 2006, discloses an engine hydraulic mounting system with a switchable valve to avoid bulging of the main elastomeric unit. A two-stage isolation mount assembly is disclosed in U.S. Pat. No. 7,048,265, issued on May 23, 2006, to Anand Huprikar, to take advantage of a soft spring rate with a low maximum displacement. In U.K. Patent No. 2,343,665, a hydraulically damped engine mounting arrangement having two load-bearing mounts and two tie bars is disclosed.
None of the known prior art references teach a hydraulic body mount device that can be attached to a conventional shear-type body to frame mounting assembly to provide a tunable vibration damping function in which the conventional body to frame mounting assembly absorbs the high vehicle loads while the plug-in hydraulic body mount provides a supplemental damping effect to the conventional body to frame mounting assembly.